Patent GB-806057-A (GB)
Title: Improvements in aircraft instruments
Inventor: MEREDITH FREDERICK WILLIAM
IPC: B64D45/00
Filed: 1956-03-01
Abstract: 806,057. Aircraft instruments. SMITH & SONS (ENGLAND) Ltd., S. March 1, 1957 [March 1, 1956], No. 6510/56. Class 4. [Also in Group XX] An aircraft instrument has an index displaceable from a datum in accordance with normal plane absolute acceleration (being the OZ component of a total acceleration excluding that due to gravity) and a further index displaceable from the datum in accordance with a demanded value (as to both magnitude and direction) of the normal plane absolute acceleration (a two component vector, being the component perpendicular to the OX axis of a demanded total acceleration excluding that due to gravity). The pilot flies the aircraft to superimpose the indices; banking rotates the direction of the demanded normal plane acceleration, and pitching varies the magnitude of the actual normal absolute acceleration. Fig. 6 shows the instrument comprising a datum line 1 fixed on a transparent screen and representing the aircraft lateral axis. An index 2 behind the screen comprises a circle and " tail " (more clearly shown in Fig. 4) on a wire 8 passing over pulleys 9 and 10, and anchored at one end to fixed structure 12 through a spring 11. The other end is wound on a reel 7 rotatable by a servo 6 controlled by a normal accelerometer 5. The disposition is such that in steady flight, (normal absolute acceleration equal to g and directed upwardly) the end of the " tail " of index 2 is on the centre of datum 1. The background to index 2 is a roller blind 16 marked with a horizon line 3. The blind runs over a driving roller 14 and idler roller 15, these being mounted on a carriage 13 to which a gear wheel 21 is secured. A gyro vertical 18 provides an angle of bank signal fed to a servo 17 driving a shaft 19 and gear 20 meshing with gear 21 to rotate the carriage and horizon line 3 about the fore-and-aft axis of the instrument. An angle of pitch signal is fed to a servo 25 driving one input of a differential 23, the other being from a gear 22 on shaft 19. The differential drives the roller 14 through shaft 26 and gears 27, 28, 29. The gear ratios are such that rotation of shaft 19 does not rotate gear 27 relatively to the carriage, whereby rotation of the carriage does not interfere with pitch indication. Between index 2 and the roller blind 16 is a spot index 4 on an endless cord 30 passing over pulleys 31, 32, 34 on a ring gear 33 driven through gear 39 by a servo 40. The cord is attached to a peg 35 mounted on a ring gear 37 driven through gear 42 by a servo 44. The peg works in a slot 38 in gear 33. To control the servos 40, 44, signals from a gyromagnetic compass 45 and radio device 46 are fed to a computer 47 which derives a heading error signal fed to a resolver 53. Signals from an airspeed responsive device 48 or radio device 49, and from a gyro vertical 52 are fed to a computer 50 which derives a pitch error signal. This signal and signals from gyro vertical 52 are also fed to resolver 53 and the outputs thereof are fed to a further resolver 41 deriving the displacement of index 4 from the datum line 1 (the demanded normal plane absolute acceleration) in polar co-ordinates. The angular co-ordinate signal energizes servo 40. so that wire 30 is rotated correspondingly about the instrument axis, and both co-ordinates are combined in a differential 43, the resultant energizing servo 44, so that the relative movement of gears 33 and 37, which determine the radial distance of spot 4 from the datum 1, is determined by the radial co-ordinate signal from resolver 41. In operation the pilot must bank the aircraft until the index 4 is in vertical alignment with index 2, and pitch the aircraft until index 2 lies over spot 4. Fig. 4 shows the appearance of the instrument when the aircraft is flown correctly to superimpose the indices, the aircraft then having an angle of bank of forty five degrees, and zero angle of pitch e.g. when the demand is for a steady turn. As an alternative, the horizon line 3 may be fixed and the index 1 movable to display the angles of bank and pitch.